Measuring apparatus

ABSTRACT

A measuring apparatus for measuring color characteristics of an object is provided. The apparatus includes at least two measuring units, each of which has at least one optical emitter and at least one optical receiver, wherein the measuring units are combined to form a measuring arrangement. The emitter has an illuminating angle and the receiver has a receiving angle, wherein relative to the object these angles are different for each measuring unit. Respective light guide terminals are provided for each measuring unit. A light source is connectable in common for at least two measuring units via a light guide and a light guide terminal. A detector is connectable in common for at least two measuring units via another light guide and light guide terminal. The light guide terminals can be selectively coupled with the light source and the detector.

BACKGROUND OF THE INVENTION

The invention relates to a measuring apparatus having at least onemeasuring unit, which in turn is provided with at least one opticalemitter and at least one optical receiver, and at least one lightsource, which is connected with the measuring unit via a light guide, aswell as a detector that is connected with the measuring unit via a lightguide.

Known color-measuring systems have a single fixed emitter and receiverarrangement. In this connection, conventionally only one light sourceand only one detector are used. The illumination is frequently effectedwith halogen light sources or xenon light sources in a pulse orcontinuous mode operation. The light source illuminates the sample to bemeasured directly, although it is generally coupled to a light guide.The light guide then illuminates the probe either directly via a roundfiber bundle, an annular light arrangement of fibers, or a plurality offiber bundles that illuminate the sample to be measured from differentdirections. It is furthermore known to columnate or parallelize thelight exiting the light guide via an optical emitter in order to achievea defined direction of illumination. As detectors, often either threephotocells having appropriate optical filters are utilized pursuant tothe three-region method, or a three-element photocell havingvapor-coated optical filters is used. It is furthermore known to usespectral photometers having a rotary grid, or to use diode line-scanningor CCD line-scanning spectrometers having a fixed grid. The coupling ofthe detector is generally effected via a light guide. In thisconnection, an optical measuring head for parallelization, that is alsodesignated as a receiving measuring head, could be disposed between thesample to be measured and the light guide. With the known arrangements,only one fixed illumination and receiving geometry is utilized for thecolor measurement at the sample.

Furthermore known are measuring apparatus for color-measuring systemsthat, at a number of angles, measure characteristics, in particular thecolor of an object that is to be measured. With one type of the knownmeasuring systems, the measurement is effected either with a fixedillumination angle and a plurality of fixed receiving angles, or with afixed receiving angle and a plurality of fixed illumination angles.Measuring systems of this type of construction are particularlyunsuitable for use when measuring the angle-dependent colorcharacteristics of novel lacquers and colors. For an adequatecharacterization of the colors, neither a single illumination angle nora single receiving angle can be fixedly prescribed. This generally meansthat a plurality of detector units, such as, for example, spectrometers,and possibly also a plurality of illumination units, must be utilized,which leads to higher costs due to the increased expenditure forcomponents. Furthermore, all of the measuring geometries must besimultaneously disposed over the sample, as a result of which thegeometric possibilities for the arrangement of the measuring heads islimited, and not all desired illumination angles and receiving anglescan be measured.

With a second known type of measuring system, the illumination angle andthe receiving angle can be adjusted manually or in a motorized manner.Such a goniometer offers the possibility of setting any desiredillumination angle by two movable measuring heads.

However, goniometers are difficult to adjust and, due to thesusceptibility to adjustment, they can be used only or laboratorypurposes, but not for routine production controls. Furthermore, theexpenditure for apparatus for automated goniometers having motor controlis high, as a result of which the apparatus are expensive. Furthermore,generally light sources and detectors are coupled to the measuring headsvia light guides, so that a movement of the measuring heads leads to analteration in the bending curves of the light guides and changes in thespectral transmission of the optical fibers occurs. Therefore, imprecisemeasurements result with goniometers due to a movement of the measuringheads relative to the light source and the detector, which have adisadvantageous effect upon the precision of the color valuedetermination.

Due to the increasing use of lacquers and colors having angle-dependentcolor characteristics, i.e. a color characteristic that is a function ofthe illumination angle as well as of the viewing or receiving angle, thedemand for precise multiple-angle color measuring apparatus isincreasing.

It is therefore an object of the invention to provide a measuringapparatus with which the above-mentioned drawbacks of conventionalmeasuring systems are avoided, and in particular to enable adetermination that is as precise as possible of the colorcharacteristics as a function of the angle and to accomplish this atdifferent illumination and receiving geometries.

SUMMARY OF THE INVENTION

The stated object is realized pursuant to the inventive measuringapparatus in that at least two measuring units are combined to form ameasuring arrangement, the measuring units each have light guideterminals, and these terminals can be selectively coupled with a lightsource, which is connectable in common for at least two measuring units,or with a detector, which is connectable in common for at least twomeasuring units.

It is advantageous if the illumination and receiving angle of theemitter and receiver of a measuring unit are different relative to anobject to be measured for each measuring unit, in order to realizedifferent illumination and receiving angles for the color measurement inone and the same measuring apparatus.

A further advantage of the present invention is that each emitter andeach receiver of a measuring unit is respectively connected via anemitter or receiver light guide with the respective terminal of themeasuring unit, and these light guides are advantageously rigidlydisposed in the measuring unit. Thus, when the entire measuring unitmoves, there is no change of the bending curves of the light guides,which otherwise could lead to changes in the spectral transmissions ofthe optical light guides and have a disadvantageous effect upon theprecision of the color value determinations.

Pursuant to a further very advantageous embodiment of the invention, thelight source and detector light guides are coupled with the respectiveterminal of a measuring unit in a contact-free manner. By shifting themeasuring units, a coupling between the light source and detector lightguides on the one hand, and light guides of different measuring units onthe other hand, is made possible, which is designated as fibermultiplexing.

It is advantageous to provide an optical coupling device between thelight source and detector light guides on the one hand, and the terminalof the measuring unit on the other hand. This enables a precise andreliable coupling between the light guides.

A further very advantageous embodiment of the invention results if themeasuring arrangement is movable relative to the object that is to bemeasured. By moving the measuring units that are combined in themeasuring arrangement, any desired measuring unit can be moved to thesample. This is designated as measuring head multiplexing.

Pursuant to a further advantageous embodiment of the invention, themovement of the measuring arrangement is linear or alternatively is arotational movement.

During movement of the measuring arrangement, the light source anddetector light guides are preferably coupled with respective terminalsof different measuring units to ensure the aforementioned fibermultiplexing.

Pursuant to one embodiment of the invention, the respective measuringunit is disposed at the same location relative to the object beingmeasured during the measuring process. This ensures that merely specificillumination angles and receiving angles of the measuring unit are theonly variable measuring parameter.

Pursuant to a further advantageous embodiment of the invention, themeasuring units of the measuring arrangement are disposed in a circularmanner, which enables a movement of the measuring units via a rotationalmovement.

Pursuant to a further embodiment of the invention, the measuring unitsof the measuring arrangement are disposed linearly in order to shift themeasuring units by a linear, transverse movement.

A further very advantageous embodiment of the invention exists if aplurality of light sources can be coupled with the measuring units viarespective light guides, thereby achieving a greater flexibility duringthe construction.

Pursuant to a further embodiment, a plurality of detectors areadvantageously coupled with the measuring units via respective lightguides in order to simultaneously read different measuring parameters ofseveral measuring units and/or different measuring units.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, as well as further embodiments and advantages, will beexplained subsequently with reference to the figures;

FIG. 1 a schematic view of one embodiment of the inventive measuringapparatus,

FIG. 2 an embodiment of the arrangement of measuring units in ameasuring apparatus

FIG. 3 a sketch of a further embodiment of the measuring apparatus.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, a measuring apparatus 1 for the angle-dependentmeasurement of color characteristics of lacquers and colors isdescribed. The measuring apparatus 1 has a plurality of measuring units2, which are combined to form a measuring arrangement 3 (see FIGS. 2 and3). The measuring apparatus 1 is furthermore provided with a lightsource 4 and a detector 5. In the preferred embodiment, the light source4 is a halogen light source 4 that couples light in one end 15 of alight guide 6. The light guide 6 serves as an illuminating fiber, and atits other end 7 can be coupled with a light guide 8 of a measuring unit2. In the preferred embodiment, the detector 5 is a diode line-scanningspectrometer. The spectrometer 5 is coupled to one end 9 of a lightguide 10. The light guide 10 serves as a receiving fiber, and its otherend 11, similar to the situation with the light guide 6, is coupled to alight guide 12 of the measuring unit 2.

The measuring unit 2 includes two optical measuring heads, anilluminating measuring head or emitter 13 and a receiving measuring heador receiver 14. The emitter 13 is connected with an emitter light guide8 at the reference numeral 19, whereby the emitter light guide 8connects the emitter with light guide terminals 16, 17 of the measuringunit 2. Similarly, the receiver 14 is connected with one end 18 of areceiver light guide 12, whereby the receiver light guide 12 leads to alight guide terminal 17 of the measuring unit. With appropriatepositioning of the measuring unit 2, the ends 7,11 of the light sourceand detector light guides 6,10 are disposed ahead of the correspondingends 16,17 of the emitter and receiver light guides 8, 12. In thisconfiguration, light from the light source light guide 6 is coupled intothe emitter light guide 8, and light from the receiver light guide 12 iscoupled into the detector light guide 10. Pursuant to a furtherembodiment of the invention, instead of a direct coupling of the fiberends 11, 6 and 12, 10 to one another via a slight spacing, the couplingcan also be effected via imaging optics.

With appropriate coupling of the emitter 13 to the light source 4, thelight exiting the emitter light guide 8 is parallelized or columnated inthe emitter 13 via an optical device 20, and illuminates, at art angleα, an to object 21 that is to be measured and that is located in frontof the measuring unit 2. A portion of the light deflected back at theobject 21 impinges upon the receiver 14 at an angle β, and is focused byan optical device 22 of the receiver 14 to the end 18 of the receiverlight guide 12. With appropriate coupling of the receiver 14 to thedetector 5, the light reflected from the object to be measured is guidedto the detector 5, where it is spectrally measured. The color values canthus be determined as a function of the illuminating angle α and thereceiving angle β.

As already mentioned previously, in principle any number of measuringunits 2 can be provided. The measuring units 2 that are combined to formthe measuring arrangement 3 can, as illustrated in FIG. 2, form a stack.Pursuant to a further embodiment of the present invention, the measuringunits 2 are disposed in a ring-shaped manner, as shown in FIG. 3, toform the measuring arrangement 3. In principle, the measuring units 2have the same construction, although they differ with regard to theilluminating and receiving angles of the emitter 13 and of the receiver14 relative to the object 21 to be measured for each measuring unit 2.The measuring arrangement 3 is arranged so as to be movable, and can betransversely moved as an entire rigid unit by a linear unit 23 in the zdirection (see FIG. 1), i.e. perpendicular to the plane of the drawingsheet. As a result of this transverse movement, any desired measuringunit 2 can be moved below the object 21 to be measured (also known asmeasuring head multiplexing), whereby due to this displacement, at thesame time the free light guide ends 16,17 of the emitter and receiverlight guides 8,12 of the measuring unit 2 are coupled to the lightsource and detector light guides 6,10 (which is designated as filamentmultiplexing).

Instead of a linear unit for the aforementioned combination of measuringhead multiplexing and fiber multiplexing, it is also possible to use arotary, unit (not shown) that rotates a measuring arrangement 3 such asthat shown in FIG. 3. In this connection, however, the maximum number ofmeasuring units 2 is limited by the 360° overall angle of rotation thatis available.

The measuring apparatus 1 described above thus offers the possibility torapidly, and possibly also automatically, switch between differentmeasuring geometries. By means of a displacement of the measuringarrangement 3, different measuring units 2 are coupled with the detector5 and the light source 4, and are used for the measurement.

In contrast to conventional measuring systems, the components of eachmeasuring unit 2 form a rigid unit. In particular, the emitter andreceiver light guides 8, 12 are fixedly mounted within the measuringunit 2. This ensures that during a movement of the measuring arrangement3, no alteration of the bending curves of the emitter and receiver lightguides 12, 8 are produced. The inventive measuring apparatus 1 thusenables a multiple angle color measurement by the use of theindividually configured measuring units 2, without thereby causingchanges in the bending curves of the light guides by possible changes ofthe positions thereof. Changes in the spectral transmissions of thelight guide 6, 10, 8, 12, which would have a negative impact upon theprecision of the color value determination, are thus precluded.

Pursuant to the above preferred embodiment, advantageously merely onelight source 4 and one detector 5 can be selectively coupled to allmeasuring units 2. Pursuant to further embodiments of the invention,however, a plurality of light sources 4 and detectors 5 can preferablybe coupled via respective light guides to the measuring units 2 andtheir respective terminals 16, 17 to provide different types of luminoussources 4, different detectors 5 for measuring a plurality ofparameters, and/or for providing redundancy in a measurement.

The specification incorporates by reference the disclosure of Germanpriority document 101 03 163.7 filed Jan. 19, 2001 and PCT/EP02/00322filed Jan. 15, 2002.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

1. A measuring apparatus, for measuring color characteristics of anobject that is to be measured, comprising: at least two measuring units,each of which has at least one optical emitter and at least one opticalreceiver, wherein said measuring units are combined to form a measuringarrangement, wherein said optical emitter has an illuminating angle andsaid optical receiver has a receiving angle, and wherein relative tosaid object that is to be measured, said illuminating angle and saidreceiving angle are different for each measuring unit; respective firstand second light guide terminals for each of said measuring units; alight source that via a first light guide and said first light guideterminal is connectable in common for at least two measuring units; anda detector that via a second light guide and said second light guideterminal is connectable in common for at least two measuring units,wherein said first and second light guide terminal, are adapted to beselectively coupled with said light source and said detectorrespectively.
 2. A measuring apparatus according to claim 1, wherein arespective emitter light guide and receiver light guide are provided forconnecting each optical emitter and each optical receiver of a measuringunit with the respective first and second light guide terminals.
 3. Ameasuring apparatus according to claim 2, wherein said emitter andreceiver light guides of a given measuring unit are rigidly disposedtherein.
 4. A measuring apparatus according to claim 1, wherein at leastone of said first and second light guides is coupled in a contact-freemanner with the respective first and second light guide terminal of agiven measuring unit.
 5. A measuring apparatus according to claim 1,wherein an optical coupling device is provided between said first andsecond light guides on the one hand, and said light guide terminals of agiven measuring unit.
 6. A measuring apparatus according to claim 1,wherein said measuring arrangement is movable relative to said objectthat is to be measured.
 7. A measuring apparatus according to claim 6,wherein said movement is linear.
 8. A measuring apparatus according toclaim 6, wherein said movement is a rotational movement.
 9. A measuringapparatus according to claim 6, wherein during a movement of saidmeasuring arrangement, said first and second light guides are coupledvia respective first and second light guide terminal with different onesof said measuring units.
 10. A measuring apparatus according to claim 1,wherein during a measuring process, a respective one of said measuringunits is disposed at the same location relative to an object that is tobe measured.
 11. A measuring apparatus according to claim 1, whereinsaid measuring units of said measuring arrangement are arranged in acircular manner.
 12. A measuring apparatus according to claim 1, whereinsaid measuring units of said measuring arrangement are arranged in alinear manner.
 13. A measuring apparatus according to claim 1, wherein aplurality of light sources are adapted to be coupled with said measuringunits via respective light guides.
 14. A measuring apparatus accordingto claim 1, wherein a plurality of detectors are adapted to be coupledwith said measuring units via respective light guides.